How to get custom URL format for Pages?

I’ve set up my ideal blog page URL format by using the custom format:
/%post_id%/%postname%.html

This gives me what I consider the best format for my content, in the form:
https://www.example.com/76/the-actual-post-title.html

However, there is no way I can see to get this format on the static Pages. I would like the html fileformat suffix, to maintain continuity, but I can’t see an obvious way to do this. For example you can’t edit the Permalink format to do this — the shape is basically excellent but it’s not possible to add a .html suffix. The dot is removed and you simply get html appended as part of the URL.

What I have is for example:
https://www.example.com/about

What I want is:
https://www.example.com/about.html

What I get, in error, is:
https://www.example.com/abouthtml

Any solution please? ??